EP1414610A1 - Unite de soudage par resistance et procede de commande correspondant - Google Patents

Unite de soudage par resistance et procede de commande correspondant

Info

Publication number
EP1414610A1
EP1414610A1 EP02760241A EP02760241A EP1414610A1 EP 1414610 A1 EP1414610 A1 EP 1414610A1 EP 02760241 A EP02760241 A EP 02760241A EP 02760241 A EP02760241 A EP 02760241A EP 1414610 A1 EP1414610 A1 EP 1414610A1
Authority
EP
European Patent Office
Prior art keywords
robot
workpiece
welding gun
electrode
welding
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP02760241A
Other languages
German (de)
English (en)
Other versions
EP1414610B1 (fr
Inventor
Simon Dietrich
Peter Rippl
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
KUKA Systems GmbH
Original Assignee
KUKA Schweissanlagen GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by KUKA Schweissanlagen GmbH filed Critical KUKA Schweissanlagen GmbH
Publication of EP1414610A1 publication Critical patent/EP1414610A1/fr
Application granted granted Critical
Publication of EP1414610B1 publication Critical patent/EP1414610B1/fr
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/30—Features relating to electrodes
    • B23K11/31—Electrode holders and actuating devices therefor
    • B23K11/314—Spot welding guns, e.g. mounted on robots
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/24—Electric supply or control circuits therefor
    • B23K11/25—Monitoring devices
    • B23K11/252—Monitoring devices using digital means
    • B23K11/253—Monitoring devices using digital means the measured parameter being a displacement or a position
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/24—Electric supply or control circuits therefor
    • B23K11/25—Monitoring devices
    • B23K11/252—Monitoring devices using digital means
    • B23K11/255—Monitoring devices using digital means the measured parameter being a force

Definitions

  • the invention relates to an electrical
  • Resistance welding device preferably an electrical spot welding device, and a method for its control, in particular adaptation for the relative position of the welding gun and workpiece, with the features in the preambles of the main method and device claim.
  • the resistance welding device is arranged stationary or is moved by a robot or another manipulator. It has a welding gun with usually two electrode arms, one of which is arranged relatively stationary and the other relatively movable and is moved by means of an arm drive in addition to a control. Suitable electrodes with replaceable electrode caps are located at the ends of the electrode arms.
  • the arm drive is controlled by force or torque.
  • the welding gun and the workpiece are each guided by a robot.
  • the welding gun must be open.
  • the welding gun must be positioned so that the tip of the electrode mounted on the fixed arm is at a minimum distance from the workpiece. This point in space is programmed (taught) in the robot's motion program and approached by the robot.
  • the minimum distance must exist for various reasons, for example due to tolerances in the position of the workpiece, due to batch tolerances of the sheets and due to tolerances of the clamping device or due to differences in length of the
  • Electrodes for example due to wear or cap milling.
  • the electrode mounted on the fixed arm of the welding gun must touch one side of the workpiece and the electrode mounted on the movable arm must touch the other side.
  • the welding gun must be closed while the robot is standing. Without additional compensation measures, deformations would occur when closing the welding gun to the fixed and from
  • Clamp compensation systems used. These are available in different versions, for example as mechanical, pneumatic, hydraulic and electromotive systems. Depending on the type of drive, the various tong compensation systems contain relatively complex components and controls. The main task of a
  • Clamp compensation system is the separation of the rigid, mechanical connection between the hand flange of the robot and the welding gun for the time the welding gun is closed until the gun opens again. Outside of this time, the welding gun must be rigidly coupled to the robot again. The mechanical decoupling of the welding gun from the robot interrupts the flow of force from the gun to the robot. Put simply, the welding gun is activated with the
  • Robot kinematically connected only via a joint In order to prevent the weight of the welding gun from being supported on the workpiece with this joint function and thereby causing an asymmetrical electrode force, the gun compensation system must also have one
  • the clamp compensation systems have major disadvantages. They increase the investment costs through more or less complex technology, increase the weight of the welding guns, require a complex and position-related adjustment of the weight balance as well as cyclical control and, if necessary, correction of this adjustment. Intensive maintenance is also necessary. The synchronization of the gun drive must with the
  • Differential drive can be synchronized.
  • the electrodes can also assume an undesirable misalignment on the workpiece during welding due to the compensation of the pliers.
  • the invention solves this problem with the features in the main method and device claim.
  • the welding gun can be mechanically rigidly connected to the hand flange of the robot, the fixed electrode arm and the associated electrode being fixed relative to the hand flange.
  • the structural design and the function of the adaptation device It is also possible to retrofit or retrofit existing welding guns.
  • the adjustment method and the adjustment device can also be used advantageously for other purposes.
  • the workpieces can be measured precisely and automatically in their position and their dimensions as well as their geometry, whereby the measurement data can be documented, saved and evaluated in different ways.
  • the robot with the guided part, preferably the welding gun is thus converted online into a measuring machine during production. In this way, the welding quality and component quality can be specifically and verifiably optimized.
  • the positioning device e.g. a robot, in which its infeed movements are calibrated.
  • Adjustment steps with wear absorption of the electrodes and according to the position or the dimensions of a workpiece can advantageously be used in connection with any arm drives.
  • Position control of the arm drive has the advantage that the resistance welding device can be controlled better and more precisely.
  • the elasticity of the welding gun between the arm drive and electrodes can be compensated. This also allows a very specific desired electrode force to be set precisely.
  • the position control enables fast and precise electrode force control, whereby force profiles can also be run. In particular, the electrode force can also be reduced during the process.
  • Position control is suitable for any type of arm drive, with particular advantages for an electric motor drive.
  • the position control also compensates automatically and quickly the spread of the mechanical properties of the pliers system, that is, geometric tolerances, mechanical friction, mechanical play and the like. Furthermore, the changes in the mechanical properties of the pliers system caused by the influence of temperature are automatically and quickly compensated for. The same applies to changes caused by aging and / or wear. Normal changes in state, such as changes in the length of the electrode caps due to wear and tear or as a result of milling, are also taken into account.
  • the position control for the welding gun can be used with any type of such devices or gun systems, whereby these can also be arranged in a stationary or movable manner. There are particular advantages with a robot-guided
  • Robot controller connected or even integrated into this. This allows the current drive or motor position to be measured very quickly and the data to be calculated quickly and directly and converted into control and movement commands.
  • the welding gun or its arm drive can be calibrated according to a desired electrode force. If the welding gun is force-controlled or force-controlled using a force meter on the gun arms, the force meter can be calibrated and calibrated to the actual electrode force.
  • the set positions of the arm drive correspond exactly to the desired electrode force due to the calibration. Suitable for calibration especially a stationary or moving force sensor, on which the moving or stationary welding gun is closed.
  • a calibration can also be carried out after the electrodes have worn, whereby electrode erosion and other shortenings of the electrodes are recorded and taken into account in the position control in the welding operation.
  • FIG. 1 a welding station with several resistance welding devices and robots as well as calibration devices in a perspective view
  • Figure 2 a resistance welding device with robot, workpiece and service device with
  • Figure 3 the arrangement of Figure 2 with the robot in calibration graduation
  • FIG. 4 a side view of a C welding gun with a fixed and a movable gun arm
  • FIG. 5 an X welding gun in side view
  • FIG. 6 a schematic representation of the caliper calibration with a sensor
  • FIG. 7 a representation of the electrode position on a workpiece
  • Figure 8 to 12 Diagrams of the individual steps in caliper calibration
  • FIG. 13 and 14 an electrode tongs in contact
  • Figure 15 a variant with distance measurement
  • Figure 16 a schematic representation of a circuit for pliers adjustment with contact sensors.
  • Figure 1 shows a processing station (28) for workpieces (5), which in this case as body shells from
  • the bodywork is processed, among other things, by electrical resistance welding using several resistance welding devices (1).
  • several welding robots (3) are used, which carry welding guns (2) of the type described in more detail below on their robot hand.
  • Stationary welding guns of this type are sometimes also referred to as welding clamps. This arrangement is shown in FIG. 1 in the lower middle image area. In preferably all cases, a robot-guided relative movement takes place between the workpiece (5) and welding gun (2).
  • the welding guns (2) are equipped with several, usually two, relatively movable gun arms (6, 7), each carrying an electrode (8) at the ends and being moved by an arm drive (11).
  • the electrodes (8) can have interchangeable electrode caps (9).
  • the sheet metal layers (14, 15) are between the electrodes (8) under the influence of So-called electrode force is pressed together, the most important thing being that the correct electrode force acts at the contact point between the sheets (14, 15), because here the material is to melt through the heating of the welding current and form a welding lens.
  • the invention provides the calibration method described in more detail below, together with the calibration device (19) for the closing stroke, and an adaptation method, together with the adaptation device (17) for the positioning stroke.
  • One or more service devices (21) for the welding robots (3) can be present in the processing station or welding station (28). These include the calibration device (19) for the welding guns (2) and other components described in more detail below.
  • a resistance welding device (1) is shown schematically in FIG. It includes a moving welding gun (2), which is moved by a multi-axis swivel arm robot (3) by means of a robot controller (4) against a workpiece (5).
  • a robot (3) any other one can be used Multi-axis manipulator can be used to move and position the welding gun (2).
  • FIG. 4 shows a so-called C-gun and in FIG. 5 an X-gun.
  • the one electrode or gun arm (6) is attached to the gun housing in a relatively stationary manner.
  • the other gun arm (7) is movable relative to the first gun arm (6), e.g. linearly displaceable and is acted upon by the arm drive (11).
  • both gun arms (6, 7) of the X gun are movably and preferably rotatably mounted on the gun housing and both are acted upon by the arm drive (11).
  • the one gun arm usually the lower gun arm (7), can be clamped at least temporarily relatively stationary to the gun housing or to the hand of the robot.
  • the welding gun (2) is attached to the hand of the robot (3) using a suitable connection plate.
  • the arm drive (11) has a suitable motor, preferably an electric motor and possibly also a gear.
  • the arm drive (11) can also be designed in any other way, for example as a pneumatic, hydraulic, pneumohydraulic or other drive.
  • the arm drive (11) also has a position measuring device (12) which is designed in a suitable manner and is arranged at a suitable point on the arm drive (11). It can be designed, for example, as a rotary encoder which is integrated in the electric motor (11) or is arranged directly on the output shaft.
  • the position measuring device (12) preferably measures the angle of rotation, but can alternatively also measure distances.
  • the workpiece (5) which consists, for example, of two or more sheet layers (14, 15), is clamped between the electrodes (8) or electrode caps (9) of the gun arms (6, 7).
  • the two electrodes (8) preferably exert a certain electrode force on the workpiece (5).
  • the welding process is carried out by applying welding current of a suitable level and duration, the current profile possibly being changed and varied, for example, using a so-called current program.
  • the electrode force can change before, during and after the welding process and in particular decrease what can take place according to a force program. These changes are process-dependent and can be achieved with the resistance welding device (1) shown.
  • the movements of the gun arms (6,7) and the arm drive (11) can either be controlled or regulated according to the force or the position or the path.
  • the electrode force is, in principle, independent of the sheet thickness and the sheet tolerances.
  • the welding gun (2) e.g. on one or both forceps arms
  • the force gauges (29, 30) are located at a distance from the electrodes on the tong arms (6, 7) and are suitable, e.g. as a strain sensor, piezoelectric
  • dynamometer there can also be only one dynamometer (29), which is preferably attached to the moving gun arm (6).
  • the dynamometers (29, 30) can also be positioned at any other point on the welding gun (2), for example in the arm drive (11) or in the vicinity of the electrodes (8).
  • the arm drive (11) has a suitable computer-aided control (13).
  • the control (13) can be designed as an independent control and externally assigned to the welding gun (2) or integrated into it or the arm drive (11).
  • the controller (13) is connected to the robot controller (4) and can in particular be integrated into it.
  • the one or more dynamometers (29, 30) are connected to the control (13) via a suitable line (18).
  • An analog or digital force controller is integrated in the control (13).
  • the control (13) is connected via a line (18) to the position measuring device (12), e.g. the encoder.
  • An electromotive arm drive (11) can also have an integrated measuring device (20) for the motor current or the motor torque represented thereby.
  • This measuring device (20) is also connected to the controller (13) via a line (18).
  • the tong arms (6, 7) execute certain translatory and / or rotational movements relative to one another, which are determined via the displacement path or the angle of rotation of the drive (11) and in particular of the electric motor and with which
  • Position measuring device (12) measured, controlled and checked. Position control of the gun arms (6, 7) and their electrodes (8) is also possible via the position measuring device (12) and its feedback to the control (4), by the arm drive (11) for one or both gun arms (6, 7) moves until the position specified by the controller (13) is reached.
  • the position control of the gun arms (6, 7) and the electrodes (8) compensate for unknown and changing mechanical factors in the drive train, such as static and sliding friction, mechanical play and the like, as well as the elasticity of the gun arms (6, 7) , Such resistances are overcome by a higher current consumption and a higher torque of the drive motor (11).
  • the electrode arms (6, 7) are moved towards one another after the workpiece contact in dependence on the force measured by means of the force meters (29, 30) in such a way that a desired electrode force arises at the welding point.
  • the force determined by the force gauges (29, 30) is proportional to the proportional electrode force developed on the electrode (8) of the respective gun arm (6, 7), spring elasticities and the like being present in the area between the electrode (8) and the force gauge (29, 30) influencing external change factors are taken into account in the proportional ratio. They can be determined by the calibration described in more detail below.
  • both electrodes should have good contact with the workpiece (5) at the start of the welding process, the closing force of the arm drive (11) also being distributed evenly over both gun arms (6, 7), so that both electrodes (8) are pressed onto the workpiece (8) with essentially the same force. It is particularly important that the desired electrode force acts between the two or more sheet layers (14, 15) of the workpiece (5). If due to incorrect positioning between workpiece (5) and welding gun (2) only one of the two electrodes has the required contact with the workpiece (2), the electrode force acting on the welding point is insufficient, with the result of a defective weld.
  • the calibration method and an associated calibration device (19) for the resistance welding device (1) and its arm drive (11) are described below.
  • the force control and / or the position control or regulation of the welding gun (2) and other things can be calibrated here.
  • the calibration device (19) consists of a suitable sensor, in particular a force sensor (10), e.g. a piezoelectric pressure transducer, which closes between the tips of the electrode caps (9)
  • a force sensor (10) e.g. a piezoelectric pressure transducer
  • Welding gun (2) can be clamped and which directly measures the electrode force occurring between the electrode caps (9).
  • the force sensor (10) is preferably combined with an electronic evaluation device which can output force signals via a line (18).
  • the calibration device (19) can be part of a service facility (21) which is located in the working area of one or more welding robots (3). This training is particularly advantageous for mobile welding guns (2) guided by the robot (3).
  • the calibration device (19) can be mobile and is moved by the robot (3) to the welding gun (2).
  • the service device (21) can also contain further components and has a preferably common stand (35) or a frame on which these parts are arranged such that they can be easily reached by the welding robot (3) with the welding gun (2).
  • the service facility (21) can be used as an additional component
  • the cap milling device (23) can have an integrated or external cap control device (24) with which the milling result of the electrode cap (9) is checked and measured.
  • the service device (21) can also have a calibration device (25) for the TCP (tool center point), for example the tip of the electrode cap (9) on the fixed gun arm (6), of the welding gun (2). This can have, for example, a measuring contact (26) with a known absolute position, which is touched by the robot (3) with the electrode cap (9) using the adapting device (17) described below, the robot position being saved at the same time as the contact and from the difference of debit and
  • the calibration device (25) can be an optical measurement unit or the like.
  • the calibration device (19), the cap milling device (23) and the calibration device (25) can be arranged on the stand (35) so as to be able to evade in the approach direction of the robot (3) via a resilient bearing (27).
  • Cap control device (24) can be connected to the control (13) and / or the robot control (4) via electrical lines (18).
  • Welding guns (2) require calibration procedures during commissioning and then later in the production cycle.
  • the calibration device (19) can be used to calibrate one or more of the dynamometers (29, 30).
  • the welding gun (2) is closed on the force sensor (10), which emits measurement signals which represent the actually acting electrode force.
  • the control (4, 13) saves the actual force value coming from the force gauge (s) (29, 30) on the welding gun (2) on the positive edge of a first signal OUT-] of the force sensor (10) Fj_ s t ⁇ .
  • the controller (13) On the positive edge of a second signal OUT 2, the controller (13) simultaneously saves the actual force value Fj st2 transmitted by the force meter (s) ( 29, 30 ). Accordingly, further OUT signals can be used.
  • the controller (4,13) compares the measured values and then automatically (auto-calibration) calculates a new sensor characteristic of the dynamometers (29,30) based on the force values known from the calibration sensor (10) and exactly reproducible force values in the switching points (F 1 or F 2 ) etc. and the stored values (F Is t ⁇ or F ⁇ s 2 ) etc., with which the force measurement values of the force gauge ( s ) (29,30) or their evaluation is corrected in the later welding operation.
  • This calibration can be carried out several times during system operation in order to promptly compensate for changes occurring during operation due to mechanical wear, thermal influences, changes to the electrode caps (9) and the like.
  • the calibration processes can also be automated by corresponding programs in the robot controller (4) or the controller (13).
  • the calibration is also carried out when changing the cap or milling or changing the electrode caps (9).
  • certain positions of the arm drive (11) can be determined, for example certain ones Rotational positions of the armature or the output shaft, certain electrode forces are assigned.
  • the force sensor (10) is designed such that its dimension and in particular its thickness d sensor do not change, or only negligibly, under the influence of force in the direction of the electrode force. This dimension and thickness of the sensor is known.
  • the force sensor (10) preferably has two switching outputs OUTi and OUT 2 , which via lines (18) with the
  • Control (13) of the arm drive (11) are connected.
  • the two switching outputs OUT 1 and OUT 2 switch when two precisely defined force values F-] and F 2 are exceeded.
  • the output OUT 1 switches when the force F-
  • FIG. 8 shows this in the diagram.
  • the two outputs OUT 1 and OUT 2 of the force sensor (10) are connected to two edge-controlled inputs of the position control (13) and cause in
  • FIG. 9 illustrates the forceps characteristic curve that occurs when the forceps arms (6, 7) and their electrodes (8) are closed on the force sensor (10).
  • Electrode caps (9) (wear and tear, milling etc.), mechanical play in the gearbox, bearings etc. a role.
  • this generally applies after a certain electrode force has been exceeded, from which the mechanical play of the pliers system is zero.
  • P S ensor F * (P 2 -Pl) / (F 2 -Fl) + (l * F 2 -P 2 * F 1 ) / (F 2 -? 1) •
  • the thickness d B ⁇ ech of the workpiece (5) and the sheet metal layers (14, 15) to be welded is also known for each welding point.
  • the factor a and the term b are determined by the
  • the term c is preferably automatically and recalculated before each welding point.
  • the aforementioned calibration process is carried out each time the welding gun (2) is changed. It can also be repeated after each milling of the electrode caps (9).
  • the calibration process can also be used to better compensate for heat-related changes in elasticity one or more different times are repeated during the welding operation. Replacing the electrodes (8) or replacing them with electrode caps also leads to a new calibration process.
  • the calibration can additionally or alternatively also include another calibration process with which the electrode wear is compensated. This calibration process is first carried out on new and unused electrodes (8) and electrode caps (9).
  • the welding gun (2) is closed at a preselected speed, the electrodes (8) or their electrode caps (9) touching each other directly. At the moment of touching the cap, the motor current increases, which is determined by the measuring device (20).
  • Control (13) triggers on this current increase, the associated position of the arm drive (11) being simultaneously reported and stored by the position measuring device (12). By comparing the positions, the path required to close the welding gun (2) with new electrode caps is obtained from this without a workpiece (5) or plates (14, 15). Alternatively, the measurement can also be carried out using the dynamometer (s) (29,30) and the determined increase in force.
  • the closing path of the welding gun (2) increases accordingly when calibrating. This change is introduced as a correction value in the position control (13) in accordance with the variable transformation described above for FIG. 11.
  • Position control (13) then automatically compensates for the cap changes in the welding operation, so that the assignment of position and electrode force is correct.
  • the above-mentioned adjustment method and the adjustment device (17) serve to determine and adopt a welding position of the welding gun (2) and the workpiece (5) that is suitable for welding and to adapt the positioning stroke.
  • This relative position is searched for by a robot movement or by a closing movement of the positioned welding gun (2) and determined by means of a preferably contacting electrode contact or a measured electrode distance.
  • the open welding gun (2) guided by the robot (3) can be used to search for the position of the relatively stationary workpiece (5) by means of a robot movement and can be determined by determining a contact or a distance.
  • the kinematics is reversed, with the workpiece (5) moved by the robot (3) being the relatively stationary open welding gun
  • the welding gun (2) is searched.
  • the welding gun (2) or the workpiece (5) or both can be guided by a robot (3).
  • the search strategy expediently runs in the robot controller (4).
  • the welding gun (2) can also be calibrated according to the dimensions of the workpiece (5) with the adapter (17).
  • FIGS. 13 and 14 illustrate, • e.g. the two sheet metal layers (14, 15) on the
  • the welding device (1) has an adaptation device (17) which can be configured in different ways and with which a contact or a distance between the electrode (8) or the electrode caps (9) and the workpiece (5) is detected.
  • the adapter (17) is connected to the robot controller (4) via a line (18).
  • the adapter device (17) makes it possible to dispense with the pliers compensation systems previously required.
  • the welding gun (2) is then preferably mechanically rigidly connected to the hand flange (37) of the robot (3), the fixed electrode arm (6) and the associated electrode (8) also being fixed relative to the hand flange (37).
  • the robot (3) stops immediately after the contact, moving slightly beyond the contact point due to the inertia. The robot then moves back to the stored contact point, the welding gun (2) then or simultaneously being closed for welding.
  • the sought-after relative position can preferably be determined without contact and without a risk of collision between the electrode (8) and the workpiece (5). If the search is done by a
  • the adaptation device (17) is designed as an electrical contact sensor system (31) connected to the robot controller (4). It can be used in both types of search with the movement of the robot (3) or the closing movement of the welding gun (2).
  • the adapter (17) consists of at least one electrical circuit with a voltage source (32) and an electrical switch (33), e.g. a relay, which is preferably connected to the fixed, electrically insulated gun arm (6) and to the preferably earthed workpiece (5).
  • FIG. 16 also schematically shows part of the welding power supply with a e.g. low-resistance transformer (34).
  • the welding gun (2) When searching, the welding gun (2) is open or only partially closed, so that none of the electrodes (8) initially comes into contact with the workpiece (5).
  • the circuit is initially open due to the distance between electrodes (8) and workpiece (5). In the case of the touch contact of the fixed electrode (8) shown in dashed lines, the circuit is closed and the applied voltage causes a current to flow, which is the relay
  • the relay (33) switches.
  • the relay (33) switches a control circuit in the robot controller (4), which causes the associated position of the contacting electrode (8) or the axis position and the position of the robot (3) to be stored there immediately.
  • the electrode (8) on the movable gun arm (7) can be moved to the workpiece (5) when the pre-positioned welding gun (2) closes.
  • the position of the contact point determined by the aforementioned second circuit in conjunction with the controller (4, 13) and the position measuring device (12) is stored.
  • the starting position of the fixed electrode (8), which the robot (3) then moves to, is calculated from this value, taking into account the starting position of both electrodes (8) and the specified sheet thickness, whereby the welding gun (2) can be closed afterwards or simultaneously for welding ,
  • Adaptation methods and the adaptation device (17) are possible in different ways.
  • the motor current and / or the motor speed and / or the can be used to determine the actual workpiece position and the determination of the sheet metal contact
  • Motor position of a preferably electric arm drive (11) or the robot drives in connection with the robot controller (4) are recorded, stored and evaluated with a comparison circuit. With sheet metal contact, the motor current increases or decreases
  • the fixed gun arm (6) usually has no sheet metal contact, so that its dynamometer (29) shows a smaller value than the other dynamometer (30) when the movable gun arm (7) comes into contact with sheet metal.
  • the robot then moves the welding gun (2) in such a way that the fixed gun arm (6) is brought into contact with the sheet metal and both force gauges (29, 30) signal the same or different relative electrode forces. In this position the robot (3) stops and the welding gun builds up the final electrode force ⁇ for welding.
  • a multi-axis force sensor in particular an electrical load cell (36), is used as a stable intermediate flange between the welding gun (2) and the hand flange (37) of the robot (3).
  • Figure 2 illustrates this arrangement schematically.
  • the load cell (36)
  • the measured value of the sensor (36) measures the reaction of the forces from the welding gun (2) to the robot (3).
  • the measured value of the sensor (36) is initially saved at the programmed starting point. It represents the sheer weight of the pliers.
  • the welding gun (2) then closes with a small electrode force. If the welding gun (2) is in the wrong position, the measured value changes due to the leading sheet metal contact of the movable gun arm (7) and the reaction force that builds up as a result.
  • the robot (3) then moves the welding gun (2) in such a way that the measured value of the sensor (36) takes on any desired size. It should preferably be at the starting point again with the original value match, so that the welding gun (2) is positioned without reaction forces to the workpiece (5). In this position, the robot (3) stops and the welding gun (2) builds up the final electrode force for welding.
  • the distance x of a relevant electrode point, preferably the tip (TCP) of the electrode cap (9), to the workpiece (5) is measured preferably without contact by any suitable distance sensor system (38).
  • the distance sensor system (38) can e.g. be a capacitive or inductive distance sensor.
  • the distance can also be measured by an external optical sensor (39), for example.
  • the distance-measuring sensor system (38, 39) is connected via a line (18) to the robot controller (4), which uses the measured distance and the known preprogrammed search position to determine the actual values for the welding position of the workpiece (5) and welding gun (2) and Above all, the actual position of the weldable contact point is calculated, at which the electrode (8) or electrode cap (9) should rest on the workpiece (5) for welding. This actual position is then approached by the robot (3) precisely and without problems of inertia and collision. At the same time or afterwards the welding gun (2) closes and the welding begins.
  • the above-described distance search can alternatively be carried out with kinematic reversal, with the robot (3) the workpiece (5) relative to the stationary or welding gun (2) held by a second robot.
  • Both variants of the distance search with suitable sensors (38, 39) can also be used for the search by means of the closing movement of the welding gun (2), the welding gun (2) concluding that the search position is free of collisions.
  • the aforementioned optical sensor system (39) can be used for the contact search described in the first exemplary embodiment and for establishing a contact between the electrode (8) or the electrode cap (9) and the workpiece (5).
  • Figure 13 shows this as a hint.
  • the adaptation device (17) can also be used to measure the actual thickness d B ⁇ ech of the sheet metal layers (14, 15).
  • the arm drive (11) moves the second movable electrode (8) upwards in the direction of the arrow while closing the welding gun (2). This closing movement takes place in torque mode until the component touches.
  • a second circuit, not shown, can be connected to the movable gun arm (7). The contact is established in the aforementioned manner via a relay. Alternatively, the contact can be determined via an increase in the motor current in the arm drive (11) and determined by the measuring device (20).
  • Position measuring device (12) determined and stored. This closing path is compared with the previously determined closing path of the electrodes (8) without sheets. The path difference represents the actual thickness d B ] _ ech of the sheet layers (14, 15). With a good fit of the sheets (14, 15) as in FIG. 13, the measured sheet thickness d B ] _ ech matches the specified value.
  • Welding gun (2) which was based on a component specification, can then remain. Otherwise, if the actual sheet thickness deviates from the specified value, a corresponding correction of the position control (13) is necessary.
  • the measured sheet thickness value d B ] _ ech is measured at the welding point and used for the possible correction of the position control (13).
  • the distance to be covered by the welding gun (2) can be increased or the end position of the arm drive (11) to be controlled can be shifted so far that the gap (16) is closed and the bent sheets (14, 15) are brought into contact become.
  • the arm drive (11) Due to the position control of the arm drive (11), the restoring force or stiffness of the bend and of the sheets (14, 15) is irrelevant and does not need to be determined either.
  • the arm drive (11) only has to be strong enough to bridge this resistance. With a force-controlled welding gun (2), this can be different and require corrections.
  • the sheet thickness d- B i ech determined in this calibration step can also be determined in the robot controller (4) and in the positioning of the welding gun (2) by the robot (3) be taken into account.
  • the robot (3) can reposition the welding gun from the previously described detected position (fixed gun arm (6)) by half the sheet thickness of the d- sheet .
  • the determination of the position of the upper plate (14) was also largely without force, the elasticities of the fixed gun arm (6) occurring in actual welding operation not being taken into account and are now dealt with by repositioning. If the welding gun (2) is not added in the manner described above, this can happen
  • the welding gun (2) can be viewed and used as a measuring machine, the measurement data preferably being in the robot controller (4) using a suitable analysis and
  • the actual dimensions of the sheet thickness or the gap (16) are known.
  • the nominal thickness of the sheets (14, 15) is also known.
  • a statement can be made by means of a corresponding evaluation Quality of the workpieces (5) to be welded.
  • early deviations can be influenced on the pre-production of the workpieces (5) or the actual production can be stopped.
  • a preferably automatic welding sequence optimization and / or a welding parameter adjustment can be carried out in order to reduce the influence of the fit on the welding quality.
  • a statistical process control is also possible, which can be used, for example, for quality control and proof of quality, for example with regard to welding quality and component geometry.
  • Online documentation of the measured values can also be used for the fit documentation as the basis for component optimization. If different workpieces (5) are welded in the mix of types, it can also be determined whether the correct workpiece or a component is available for welding (e.g. with different material thicknesses).
  • the maximum permissible force of the gun can also be monitored. If this should be exceeded, a good weld can be achieved by changing other welding parameters (current, time, etc.) without overloading the welding gun (2).
  • Exemplary embodiments and the method steps are possible in various ways.
  • Individual calibration and adjustment processes can be replaced by entering empirically obtained correction values in the position control. With these correction values, for example, electrode cap wear, a change in elasticity due to temperature shifts, or other external changes Influences are compensated. This is possible above all if these influences change substantially evenly during welding and can be recorded as empirical values with sufficient reliability.
  • These correction values can be entered periodically in a stepper function in the position control (13). This can take place during breaks in operation, but alternatively also during the welding operation.
  • the calibration method and the calibration device (19) can also be dispensed with and a conventional technique can be used instead.
  • the design of the resistance welding device (1) and its components as well as the robot (3) are also variable.
  • a welding gun with two or more gun arms (6,7) a welding picker with only one picker arm can be used, which presses its electrode against a solid surface or an abutment.
  • the pliers or clamp geometry and kinematics can also be variable.
  • the electrode (s) can have any shape and configuration. Exchangeable electrode caps (9) can be omitted if necessary.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Robotics (AREA)
  • Resistance Welding (AREA)

Abstract

L'invention concerne un procédé et un dispositif servant à commander et notamment à ajuster une pince porte-électrode (2) de soudage par résistance. La position relative de la pince porte-électrode (2) et de la pièce (5) est déterminée et ajustée par un robot (3), selon un procédé d'ajustement, pour permettre le soudage. Au cours d'un mouvement de recherche relatif, un contact ou un écartement entre une électrode (8) et la pièce (5) est recherché ou déterminé. Les données de mesure de force ou de position correspondantes sont simultanément enregistrées et comparées dans l'organe de commande de robot (4), la position relative correcte étant déterminée à partir des données de comparaison, puis la pince porte-électrode est amenée dans ladite position correcte. Le contact entre l'électrode (8) et la pièce (5) est déterminé de préférence au moyen d'un système de détection de contact électrique (31).
EP02760241A 2001-07-12 2002-07-12 Unite de soudage par resistance et procede de commande correspondant Expired - Fee Related EP1414610B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE10133297 2001-07-12
DE10133297 2001-07-12
PCT/EP2002/007776 WO2003008146A1 (fr) 2001-07-12 2002-07-12 Unite de soudage par resistance et procede de commande correspondant

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EP1414610A1 true EP1414610A1 (fr) 2004-05-06
EP1414610B1 EP1414610B1 (fr) 2008-03-19

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EP02751136A Expired - Fee Related EP1409190B1 (fr) 2001-07-12 2002-07-12 Dispositif de soudage par resistance et procede de commande associe

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WO (2) WO2003008145A1 (fr)

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Also Published As

Publication number Publication date
DE50201529D1 (de) 2004-12-16
WO2003008145A1 (fr) 2003-01-30
DE50211924D1 (de) 2008-04-30
WO2003008146A1 (fr) 2003-01-30
EP1409190A1 (fr) 2004-04-21
EP1414610B1 (fr) 2008-03-19
EP1409190B1 (fr) 2004-11-10

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